Treatment of cellulose esters containing colloiding agents



Jan. 19, 1937. 2,067,937

TREATMENT OF OELLULQSE ESTERS CONTAINING COLLQIDING AGENTS p. McBURNE Y-ET Au Filed Aug 12, 1931 our H. noeeau Patented Jan. 19, 1937 TREATMENTOF OELLULOSE ESTERS CON- TAINING COLLOIDING AGENTS Dorman McBurney andEdgar H. Nollau, Newburgh, N. Y., assignors to E. L du Pont de Nemours &Company, Wilmington, DeL, a corporation of Delaware Application August12, 1031, Serial No. 550,506

7 Claims. (01. 260-133) This invention relates to a method of removingcolloiding agents from cellulose esters, and more particularly, to amethod of treating cellulose nitrate containing camphor to recover boththe cellulose nitrate and camphor.

Scrap Celluloid", French ivory, photographic film base, and the like,furnish a cheap and plentiful source of cellulose esters and of thevarious colloiding agents used in plasticizing 10 cellulose esters. Theuse of such scrap without removal of the colloiding agents is frequentlyunsatisfactory and this is particularly true where camphor has been usedas the colloiding agent, due to the characteristic odor of camphor whichis objectionable in many of the articles made from cellulose esters.Heretofore, scrap film, and the like, have been treated for the removalof camphor, but many such processes result in the destruction of thecellulose ester, especially those 2 involving treatment of the scrapwith alkali and subsequent distillation of the camphor, therebydestroying the cellulose nitrate.

An object of the present invention is to provide a. simple andeconomical process of removing colloidlng agents from cellulose esterswithout harming either the colloiding agent or the ester. A morespecific object is to provide a method of removing camphor from scrapcellulose nitrate containingcamphor to obtain both the camphor and thecamphor-free cellulose nitrate in satisfactory condition for reuse.Other objects will be apparent from the detailed description of theinvention given hereinafter.

The above objects are accomplished according to the present invention byextracting the colloiding agent from the cellulose ester by means of anextraction medium, which is an active solvent for the colloiding agentbut has merely a softening action on the cellulose ester in the presenceof the collolding agent, withdrawing the extraction medium containingthe dissolved colloiding agent, and recovering the colloiding agent fromthe extraction medium.

The extraction medium may comprise a wide variety of solvents for thecolloiding agents and may comprise a single solvent or a mixture ofseveral solvents. The solvent selected must not have any substantialsolvent efiect on the cellulose ester being treated, but it is highlyadvantageous that it should have sufficient solvent action on thecellulose ester in the presence of the colloiding agent to cause asoftening of thecellulose ester. This softening greatly facilitates theextraction .of the colloiding agent. Ethylene dichloride, propylenedichloride, carbon tetrachloride, and chloroform are all suitable assingle extraction mediums, or may be used in combination with ethylalcohol. Ethyl alcohol is also a suitable extraction medium by itselfand may becombinedwith benzol, toluene, 5 water, acetone, or ethylacetate to form a twocomponent solvent mixture, as well as with thechlorinated lower aliphatic hydrocarbons mentioned above. Where atwo-componentsolvent mixture is being employed, in which one com- 10ponent is an active solvent for the cellulose ester being treated, forexample, ethyl acetate or acetone, or where one component has nosubstantial solvent action on the colloiding agent to be extracted, forexample, water, it will be apparent 15 that the proportions of thecomponents of the solvent mixture can be varied at will.

From the disclosure of the extraction mediums given above, otheranalogous solvents, either single or two or more component mixtures,will D suggest themselves to those skilled in the art. A list ofsatisfactory two-component solvent mixtures suitable for use as theextracting medium is given below, showing the preferred proportion ofeach ingredient:

Percentages by weight Per cent Benzol 0-25 Ethyl alrnhnl -75 Toluene-0-25 Ethyl alcohol 100-75 Ethylene dichloride 100-95 Ethyl alcohol 0- 5Propylene dichloride 100-95 Ethyl alcohol 0- 5 Water 0-10 Ethyl alcohol100-90 Acetone 0- 0.5 Ethyl alcohol 100-995 Ethyl acetate 0- 0.5 Ethylalcohol 100-995 In the single figure of the accompanying drawing isshown a front elevation of an apparatus 50 suitable for carrying out thepresent invention, the apparatus being illustrated more or lessdiagrammatically.

A preferred method of carrying out the treatment of cellulose nitratefilm scrap containing 56 camphor as the colloiding agent has follows:The film scrap is placed in the wire basket i of the extraction kettle2. A suitable extraction medium, for example,- ethylene dichloride, isrun into the kettle 2 from the storage tank 2 through the pipe 4 byopening valve I until the film scrap has been covered. The still 2containing a further supply of ethylene dichloride is then heatedchloride.

until the boiling point of ethylene dichloride'is reached, the vapors ofethylene dichloride being conducted through the pipe I and sparger pipe'8 into the kettle 2. This vapor raises the temperature of the ethylenedichloride in the kettle 2 to, or near, the boiling point of ethylenedichloride, which is 83.5 C. The-temperature varies between 74-835 C.The-heating is continued for a period of from 5-80 minutes, usuallyabout 15 minutes, and any ethylene dichloride vaporized passes throughthe pipe 8 to the condenser l0 and thus through pipe ll back to thestorage tank I. The level of the ethylene dichloride in the kettle 2 iskept high enough to cover the film scrap by running additional amountsof ethylene dichloride into the kettle 2 from the storage tank 3 toreplace ethylene dichloride lost through volatilization. After theheating period, the ethylene dichloride in kettle 2 is run back into thestill 6 through pipe 12 by opening valve l3, and then removed to recoverthe camphor. The cellulose nitrate film scrap is left in the basket andsubjected to a second extraction treatment, if desired. Three extractiontreatments are sumclent in ordinary cases to remove the last trace ofcamphor from the cellulose nitrate, and even a single treatment may besumcierit in some cases.

The recovery ofthe camphor from the ethylene dichloride is convenientlyaccomplished by adding water to the solution of camphor in ethylenedichloride and distilling off the ethylene di- The camphor isprecipitated by this step, separated from the water by centrifuging, andsublimated to obtain a pure product. The recovery of the camphor fromthe ethylene dichloride solution may be carried out in other ways, aswill be apparent to those skilled in the art. The specific method ofrecovering the colloiding agent from the extraction medium forms no partof the present invention.

After the ethylene dichloride has been withdrawn from the cellulosenitrate, the cellulose nitrate may be dissolved in suitable solvents andfillers and pigments, if present, filtered out, thereby obtaining acellulose nitrate which has all the properties of the so-called virgin"cellulose nitrate.

The proportion of extraction medium to cellulose ester to be treated mayvary widely, but it has beenfound preferable to use from 1-15 parts byweight of extraction medium to one part by weight of cellulose ester.

The following example is given to illustrate a typical extraction ofcamphor from cellulose nitrate film scrap.

Example 1.-First cycle: 49.5 pounds of film scrap were placed in theextraction basket and extracted for minutes with 675 pounds of ethylenedichloride. The extraction medium was withdrawn after this period.

Second cycle: The film scrap was then extracted for 20 minutes with 525pounds of fresh ethylene dichloride, the extracting medium being againwithdrawn after this period.

Third cycle: The film scrap was again extracted for 20 minutes with 525pounds of fresh ethylene dichloride, the extraction medium beingwithdrawn after this period, and leaving a substantially camphor-freecellulose nitrate in the extraction kettle. a The approximatetemperature at which the extraction steps were carried out was 74' C.The

phor was recovered from the ethylene dioride used in the process and theextracted cellulose nitrate was dissolved and applied to a surface as acoating to see if any trace of the characteristic odor of camphorremained. It was found that the cellulose nitrate did not have theslightest trace of the characteristic camphor odor. The process of thepresent invention is applicable to cellulose acetate and other esters ofcellulose, due consideration being taken of the particular ester undertreatment, in order than an extraction medium is selectedhaving.substantially no solvent effect other than a mere softeningaction on the ester.

An advantage of the present invention is the recovery of the celluloseester having essentially the properties substantially identical withsocalled virgin cellulose esters, that is, cellulose ester which has notbeen used. The colloiding agent can be removed substantiallyquantitatively and recovered in pure form. The process is economical tocarry out and adapted for large scale operation. Where the claimsmention cam-- phor as the colloiding agent, it is to be understood thatthey include obvious equivalents thereof which are soluble withoutchemical change in the solvent recited.

While a particular preferred method of carrying out the invention hasbeen described with the use of ethylene dichloride as the extractionmedium, it is not intended that the invention be limited to the use ofethylene dichloride as the single extraction mediums, and thetwo-component extraction mediums disclosed herein are all suitable forthis purpose, as well as various other single and two-componentextraction mediums which will be apparent to those skilled in the artfrom a consideration of the solvents herein disclosed.

As many apparent and widely different embodiments of this invention maybe made without departing from the spirit and scope thereof, it is to beunderstood that we do not limit ourselves to the specific embodimentsthereof except as defined in the appended claims.

We claim:

1. In a process of purifying cellulose ester compositions containingcamphor, the improvement which comprises treating the camphor-containingcellulose ester composition with a dichlorinated saturated loweraliphatic hydrocarbon in,

such excess that the cellulose ester is not dissuch excess that thecellulose nitrateis not dissolved, withdrawing the extraction mediumfrom the cellulose nitrate, and recovering the camphor from theextraction medium.

4. Method of treating cellulose nitrate containing camphor whichcomprises extracting the camphor from the cellulose nitrate by means ofethylene dichloride in such excess that the cellulose nitrate is notdissolved at approximately the boiling point oi. ethylene dichloride,withdrawing the ethylene dichloride, and recovering the camphor from theethylene dichloride.

5. Method oi treating cellulose nitrate containing camphor whichcomprises extracting the camphor from the cellulose nitrate by immersingthe cellulose nitrate in a liquid'ethylene dichloride bath containingsuch an excess of ethylene dichloride that the cellulose nitrate is notdissolved and passing the ethylene dichloride vapors through the bathfor 5-60 minutes, withdrawing the ethylene dichloride from the cellulosenitrate, and recovering the camphor irom the ethylene dichloride.

6. Method oi. treating cellulose nitrate containing camphor whichcomprises extracting the camphor from the cellulose nitrate by means ofpropylene dichloride in such excess that the cellulose nitrate is notdissolved at approximately the boiling point of propylene dichloride,withdrawing the propylene dichloride, and recovering the camphortherefrom.

7. Process of recovering camphor and cellulose ester from celluloidscrap which comprises extracting the scrap with at least ten times itsweight of ethylene dichloride ior about 25 minutes, withdrawing thesame, and treating the scrap with a similar amount of the dichloride fora shorter period of time, and repeating until the ester is substantiallyfree of camphor.

DORMAN MCBURNEY. EDGAR H. NOLLAU.

